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Required Reading


   CSPICE_LSPCN computes L_s, the planetocentric longitude of the sun,
   as seen from a specified body.

   For important details concerning this module's function, please refer to
   the CSPICE routine lspcn_c.



      body        is the name of the central body, typically a planet.

      et          is the epoch at which the longitude of the sun (L_s) is
                  to be computed. 'et' is expressed as seconds past J2000
                  TDB (Barycentric Dynamical Time).

      abcorr      indicates the aberration corrections to be applied
                  when computing the longitude of the sun.  'abcorr'
                  may be any of the following.

                     'NONE'     Apply no correction.

                     'LT'       Correct the position of the sun,
                                relative to the central body, for
                                planetary (light time) aberration.

                     'LT+S'     Correct the position of the sun,
                                relative to the central body, for
                                planetary and stellar aberrations.

   the call:

      double = cspice_lspcn( body, et, abcorr )


      The function returns the scalar double precision planetocentric
      longitude of the sun, often called "L_s," for the
      specified body at the specified time. This is the longitude of
      the body-sun vector in a right-handed frame whose basis vectors
      are defined as follows:

         - The positive Z direction is given by the instantaneous
           angular velocity vector of the orbit of the body about
           the sun.

         - The positive X direction is that of the cross product of the
           instantaneous north spin axis of the body with the
           positive Z direction.

         - The positive Y direction is Z x X.

      Units are radians; the range is 0 to 2*pi.  Longitudes are
      positive to the east.


   Any numerical results shown for this example may differ between
   platforms as the results depend on the SPICE kernels used as input
   and the machine specific arithmetic implementation.

      Use the meta-kernel shown below to load the required SPICE


         File name:

        This meta-kernel is intended to support operation of SPICE
         example programs. The kernels shown here should not be
         assumed to contain adequate or correct versions of data
         required by SPICE-based user applications.

         In order for an application to use this meta-kernel, the
         kernels referenced here must be present in the user's
         current working directory.

         The names and contents of the kernels referenced
         by this meta-kernel are as follows:

            File name                     Contents
            ---------                     --------
            de421.bsp                     Planetary ephemeris
            pck00010.tpc                  Planet orientation and
            naif0011.tls                  Leapseconds


            KERNELS_TO_LOAD = ( 'de421.bsp',
                                'naif0011.tls'  )


      cspice_furnsh, '' 

      cspice_str2et, '21 march 2006', et
      lspcn = cspice_lspcn( 'earth', et, 'none' ) * cspice_dpr()
      print, lspcn

   IDL outputs:




Required Reading



   -Icy Version 1.0.1, 26-JAN-2017, EDW (JPL)

      Edited Example to correspond to Mice version.

   -Icy Version 1.0.0, 16-JUN-2003, EDW (JPL)


   planetocentric longitude of sun
   compute L_s
   compute Ls
   compute L_sub_s

Wed Apr  5 17:58:02 2017